Infection with HTLV-II in humans is normally determined by the ability to detect antibodies to the virus. However, it is possible that infectious virus is present prior to the appearance of those antibodies. The purpose of this study is to determine if infectious HTLV-II or HTLV- II genome can be detected in a high risk population (intravenous drug users) in the absence of detectable antibodies to the virus. Polymerase chain reaction techniques will be used to detect HTLV-II DNA and RNA in blood samples from donors. The laboratory in which these studies will be performed is being established currently and it is anticipated that results will be available in coming years.